In recent years, along with great development of living environment, a very small amount of chemical substances present in life space increasingly attract attention as causes of environmental pollution, endocrine disrupting chemicals (environmental hormones) and chemical sensitivity.
On the other hand, when a cigarette burns, it generates a granular phase and a vapor phase in its smoke, and the vapor phase contains, for example, carbon monoxide, nitrogen oxide (NOx) and ammonia and in addition, noxious substances including carbonyl compounds and organic acids, phenol derivatives such as phenol, cresol and catechol, hydrogen cyanide, sulfides represented by hydrogen sulfide, etc. Among them, carbonyl compounds attract attention as main causative substances of chemical sensitivity in recent years and are known as chemical substances harmful to the human body.
Here, carbonyl compounds are compounds having a carbonyl group (C═O) such as aldehydes and ketones. They are one of noxious gas components which are highly likely to be present in the living environment. For example, a low molecular aliphatic aldehyde is a major component among various noxious gas components contained in the cigarette smoke, and further, formaldehyde has been known as a major causative component of sick house syndrome, emitted from building material in recent years. Among noxious gas components contained in a cigarette, as carbonyl compounds, formaldehyde, acetaldehyde, acrolein, propionaldehyde, butylaldehyde, crotonaldehyde, acetone, methyl ethyl ketone, a benzaldehyde derivative of an aromatic aldehyde compound, etc. have been reported.
In order to remove such noxious gas components thereby to maintain a pleasant living environment, a gas adsorbent having high adsorptivity for noxious gas components has been required, and various gas adsorbents have been used in home life.
In general, for many of gas adsorbents, porous materials which adsorb gas in their physically porous structures, such as activated carbon, silica gel and zeolite have been widely used. However, among such porous materials, for example, silica gel easily adsorbs noxious substances such as carbonyl compounds and hydrogen cyanide but easily releases the adsorbed components as well, and is thereby known as an adsorbent having low retention properties for such noxious substances (having low adsorptivity).
Further, in a case where a gas stream having a flow rate at the same level as that when it passes through a cigarette filter is brought into contact with the surface of the porous material such as activated carbon, silica gel or zeolite, the gas adsorptivity tends to be low as compared with a case where a gas stream having a relatively low flow rate is made to pass.
The flow rate of a gas stream which passes through a cigarette filter at the time of smoking is very high, and it has been known that the flow rate is approximately from 10 to 30 m/sec and the retention time is within one second. Accordingly, when a gas adsorbent is used in a cigarette filter, it is required to have a sufficient gas adsorptivity for a gas stream having a flow rate at the time of passing through the cigarette filter. Further, also when a gas adsorbent is used not for a cigarette filter but for a gas filter of apparatus which is required to remove noxious gas in cigarette smoke such as an air cleaner or a car air conditioner, it is desired to have a sufficient gas adsorptivity for a high flow rate gas stream with a view to improving the capacity.
Patent Document 1 discloses a cigarette filter comprising a non-volatile inorganic substrate having a reactive functional group as a reagent, therein the reagent chemically reacts with a gaseous component of a smoke stream to remove the gaseous component from the smoke stream.
Patent Document 1 proposes a cigarette filter containing a silica gel having 3-aminopropylsilyl groups as the most preferred embodiment of the reagent, and that primary amino groups in the 3-aminopropylsilyl groups chemically react with and covalently bonded to noxious substances such as hydrogen cyanide and aldehydes thereby to selectively remove them. However, the cigarette filter containing the silica gel has a low amino group content, whereby its adsorption amount of noxious substances such as hydrogen cyanide is insufficient, and aldehydes are not likely to be removed. Further, in preparation of a silica gel to which propylsilyl groups are bonded as a gas adsorbent from 3-aminopropyltriethoxysilane and silica gel, unreacted 3-aminopropyltriethoxysilane will remain. The obtained gas adsorbent is dried in an oven, and if unreacted 3-aminopropyltriethoxysilane remains in a large amount in the gas adsorbent, the gas adsorbent will emit an amine odor even after drying and may influence the odor and the flavor.
On the other hand, it has been studied to use an ion exchange resin as a gas adsorbent so as to remove noxious substances. For example, Patent Document 2 discloses a multiple section cigarette filter comprising a selective adsorbent section comprising a selective adsorbent material having an affinity for a predetermined class of chemical compounds dispersed throughout a fibrous material; and a general adsorbent section comprising a general adsorbent material having a high surface area and being capable of adsorbing smoke constituents without a high degree of specificity, the selective adsorbent section and the general adsorbent section being co-axially aligned in tandem. Patent Document 2 proposes use of activated coconut carbon as the general adsorbent material having a large surface area and capable of adsorbing smoke constituents without a high degree of specificity, and Duolite A7 (tradename, manufactured by Rohm and Haas) as the selective adsorbent material having an affinity for the chemical compounds.
Duolite A7 has a phenol-formaldehyde resin matrix and is surface-functionalized with primary and secondary amine groups, thereby enhancing the resin's specificity toward the aldehydes. However, for the Duolite A7, a phenol derivate is used to form the resin skeleton, and accordingly free noxious components such as an aromatic compound derived therefrom are released. Further, according to the experimental results disclosed in Patent Document 2, the adsorption amount of acetaldehyde is not good.
Patent Document 3 discloses a cigarette filter comprising a first component which is a quick adsorbent for gaseous components in cigarette smoke containing aldehydes with low retention properties, and a second component which includes aminos and which is chemically bonded to the gaseous components to generate a substantially non-volatile reaction product, mixed or very closely dispersed. Patent Document 3 discloses, as specific examples of the second component, Duolite A7 (tradename) disclosed in Patent Document 2 also and an amino group type anion exchange resin such as DIAION CR20 (tradename, manufactured by Mitsubishi Chemical Corporation) as well.
Further, Patent Document 4 discloses a gas adsorbent which is a crosslinked polymer mainly comprising a vinylamine of which the nitrogen atom may be alkylated and a polyvinyl compound. The gas adsorbent in Patent Document 4 is a gas adsorbent which is a vinylamine type ion exchange resin comprising an aromatic divinyl compound as a crosslinkable component and which contains a vinylamine component which is directly related to gas adsorption power in a large amount.
A gas adsorbent comprising DIAION CR20 (tradename, manufactured by Mitsubishi Chemical Corporation) disclosed in Patent Document 3 and a vinylamine type ion exchange resin disclosed in Patent Document 4 is intended to increase adsorptivity for aldehydes, but such a gas adsorbent is an amino group type anion exchange resin, and amine impurities released therefrom make an amine odor, thus significantly influences the odor and the flavor. Further, since styrene or a divinylbenzene compound is used as e.g. a crosslinkable component, a free noxious component such as an aromatic compound derived therefrom is released.
Further, Patent Document 4 also discloses a process of removing an acidic gas from a gas containing an acidic gas, which comprises bringing it into contact with the gas containing an acidic gas to adsorb the acid gas, and then heating the gas adsorbent in which the acidic gas is adsorbed to disorb the acidic gas.
However, by the above process, release of the above free noxious components and amine impurities can not sufficiently be suppressed, and further, if washing with a basic aqueous solution is carried out, even amino groups in the gas adsorbent are removed, thus decreasing the effect of the gas adsorbent. Further, if washing with an acid or an alkali is carried out, formalin will form, which will remain in a vinylamine ion exchange resin to be finally obtained. It is very difficult to solve the above problems and to realize industrial mass production by the process disclosed in Patent Document 4.
Further, as described above, in general, for many of gas adsorbents to be used for a cigarette filter, porous materials which adsorb gas in their physical porous structures, such as activated carbon, silica gel and zeolite have been widely used. However, if such a porous gas adsorbent is used for a cigarette filter by itself, since adsorption selectivity is low, not only aimed is noxious gas components but also flavorous components useful for a cigarette such as nicotinamide originally contained in a cigarette or 1-menthol to be added to a cigarette are adsorbed, thus impairing the flavor of the cigarette. Accordingly, a gas adsorbent which will not impair flavorous components is desired for a cigarette.
Patent Document 1: JP-A-2002-528106
Patent Document 2: JP-A-2004-538016
Patent Document 3: JP-A-54-151200
Patent Document 4: JP-A-6-190235